Flotation apparatus and processes respond to changing conditions resulting from depletion of high grade material sources, such as coal, along with a rising demand for the material. Also, rising cost factors have increased attempts to expand the production ability of the flotation apparatus. It has been found that in the removal of the desirable materials from a slurry, it is important to mechanically treat a mass of fine air bubbles to effect a release of entrapped, unwanted material. Each flotation machine is designed to accomplish different flotation functions. Prior apparatuses of the flotation type have had some serious disadvantages. For example, prior apparatuses of relatively good efficiency have been complicated in construction, which resulted in higher cost both in assembly and in disassembly for maintenance purposes. On the other hand, apparatuses of simpler construction have not been efficient thereby increasing production cost and requiring the installation of more units for a given production requirement. All prior apparatus which produce air bubbles do not, as far as it is known, treat the air bubbles so as to remove, unwanted entrapped materials.
It has been found that the production of a mass of fine air bubbles with low rotation of the agitator, while efficient for the most part in the removal of unwanted gangue from a coal slurry mixture, has not been able to remove the entire mechanically trapped portions of gangue.